Question

How many lone pairs are on the central atom in the perchlorate ion?

Answer 1

None at all......

Explanation:

The conventional VSEPR structure of `"perchlorate ion"` is as `""^(-)O-Cl(=O)_3`. There are 7 electrons formally centred on the central chlorine atom arranged in `3xxCl=O`, and `1xxCl-O^-` bonds. The central chlorine thus has a NEUTRAL electronic count.

The three formally doubly bound oxygen atoms are each associated with 6 electrons, and are thus NEUTRAL. This leaves a `Cl-O^(-)` bond, for which the oxygen is associated with 7 valence electrons (rather than the 6 valence electrons required for neutrality; these electrons + the 2 inner core electrons balance the nuclear charge of the oxygen atoms), and thus this oxygen atom has a FORMAL NEGATIVE CHARGE.

Of course, we can draw resonance structures to show that the oxygen atoms are equivalent, and the electronic charge can be delocalized around the molecule.

In the given structure, how many (i) lone pairs are around each `=O` atom, and how many (ii) lone pairs are around the `-O^(-)` atom?